In this paper, Bayer red mud and ground granulated blast furnace slag were formed into three different ratios (7:3, 5:5 and 3:7) of alkali-activated cementitious materials (AASR) using a water glass solution as the alkali activator. By studying the compressive strength of different red mud content, the effect of Bayer red mud content on the mechanical properties of AASR was analyzed. The influence mechanism of red mud content on the mechanical properties of AASR was revealed by the variation of micro-porosity, connected porosity, Isothermal calorimetry, XRD, FTIR, and BSE/EDS testing techniques. The results show that the compressive strength of the specimens at the same age decreases with the increase of red mud content. On one hand, the addition of red mud makes the connected porosity in the AASR system increase, and the densification of the slurry structure decreases; on the other hand, the inert minerals in red mud participate in the hydration reaction to a lesser extent, the overall hydration reaction process becomes lower, and the generation of hydration products providing strength decreases.

The low mechanical strength of a low-calcium fly ash (FA)–red mud (RM) geopolymer severely limits its application. Steel slag (SS) and Ca(OH)₂ can provide calcium and alkali for the hydration process of a low-calcium FA-based geopolymer. In this study, SS was used to replace part of the RM, and Ca(OH)₂ was introduced. The effects of SS and Ca(OH)₂ on the properties of the FA-RM geopolymer were investigated. The experimental results show that SS promoted the matrix to generate more C(N)-A-S-H and C-S-H gels and optimized the pore structure, thereby improving the mechanical properties of the FA-based geopolymer. The addition of 4 wt.% Ca(OH)₂ increased the hydration products of the FA-based geopolymer, the microstructure was denser, and the mechanical properties were significantly improved. The 28 d compressive strength of the FA-based ternary composite geopolymer prepared by replacing part of the RM with SS and adding Ca(OH)₂ reached 30.6 MPa, which provided an experimental basis for the resource utilization of various bulk solid wastes.

This study investigated the effect of hollow 304 stainless-steel fiber on the corrosion resistance and mechanical properties of ultra-high-performance concrete (UHPC), and prepared copper-coated-fiber-reinforced UHPC as the control group. The electrochemical performance of the prepared UHPC was compared with the results of X-ray computed tomography (X-CT). The results reveal that cavitation can improve the distribution of steel fibers in the UHPC. Compared with solid steel fibers, the compressive strength of UHPC with hollow stainless-steel fibers did not exhibit significant change, but the maximum flexural strength increased by 45.2% (2 vol% content, length–diameter ratio of 60). Hollow stainless-steel fiber could better improve the durability of UHPC compared with copper-plated steel fiber, and the gap between the two continued to increase as the durability test progressed. After the dry–wet cycle test, the flexural strength of the copper-coated-fiber-reinforced UHPC was 26 MPa, marking a decrease of 21.9%, while the flexural strength of the UHPC mixed with hollow stainless-steel fibers was 40.1 MPa, marking a decrease of only 5.6%. When the salt spray test had run for seven days, the difference in the flexural strength between the two was 18.4%, but when the test ended (180 days), the difference increased to 34%. The electrochemical performance of the hollow stainless-steel fiber improved, owing to the small carrying capacity of the hollow structure, and more uniform distribution in the UHPC and lower interconnection probability were achieved. According to the AC impedance test results, the charge transfer impedance of the UHPC doped with solid steel fiber is 5.8 KΩ, while that of the UHPC doped with hollow stainless-steel fiber is 8.8 KΩ.

In this paper, S95 grade ultrafine mineral admixture was prepared by water quenched manganese slag and fly ash 1:1 compound mechanical ball milling to a specific surface area of 714 m²/kg. Its activity index was 86.8% at 7d and 96.3% at 28d. The S95 ultrafine mineral admixture prepared by ball milling has the characteristics of small particle size, high specific surface and high activity. Mixing with powders of different particle sizes, such as cement and silica fume, is helpful to improve particle gradation, reduce its pore structure and increase its compacting property for UHPC whose raw materials are fine aggregate. Ultra-high performance concrete (UHPC) was prepared by using the obtained ultrafine mineral admixture based on orthogonal test. The effects of different factors on the workability, mechanical properties, hydration heat and microstructure of UHPC were studied. The results show that when the silica fume content is 10%, the mineral admixture content is 10%, the binder-sand ratio is 1.1, and the water-binder ratio is 0.17, the fluidity of UHPC slurry can reach 261 mm, the compressive strength of 7d and 28d age can reach 128 MPa and 154.6 MPa, respectively. The hydration heat release of cementitious materials in 3d was 139.8 J/g. In terms of solid waste resource utilization, S95 grade ultrafine mineral admixture prepared by water-quench manganese slag and fly ash can replace 10% silica fume for the preparation of UHPC. It can not only solve the utilization problem of high added value of water quench manganese slag, but also reduce the preparation cost of UHPC to a certain extent.